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Identification of new DNA-associated proteins from Waddlia chondrophila. Sci Rep 2019; 9:4885. [PMID: 30894592 PMCID: PMC6426960 DOI: 10.1038/s41598-019-40732-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2018] [Accepted: 02/22/2019] [Indexed: 12/11/2022] Open
Abstract
Transcriptional regulation in Chlamydiae is still poorly understood. The absence until recently of genetic tools is the main cause of this gap. We discovered three new potential DNA-associated proteins of Waddlia chondrophila, a Chlamydia-related bacterium, using heparin chromatography coupled to mass spectrometry (Wcw_0377, Wcw_1456, and Wcw_1460). By ChIP-seq analysis, we determined the regulatory landscape of these three proteins and we showed that Wcw_0377 binds all along the genome whereas Wcw_1456 and _1460 possess a wide regulon with a large number of co-regulated genes. Wcw_1456 and Wcw_1460 interact with RpoD (σ66), emerging as potential RpoD regulators. On the other hand, Wcw_0377 is able to reach the host nucleus, where it might interact with eukaryotic histones through its putative chromatin-remodelling SWIB/MDM2 domain.
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Parrett CJ, Lenoci RV, Nguyen B, Russell L, Jewett TJ. Targeted Disruption of Chlamydia trachomatis Invasion by in Trans Expression of Dominant Negative Tarp Effectors. Front Cell Infect Microbiol 2016; 6:84. [PMID: 27602332 PMCID: PMC4993794 DOI: 10.3389/fcimb.2016.00084] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2016] [Accepted: 08/03/2016] [Indexed: 11/13/2022] Open
Abstract
Chlamydia trachomatis invasion of eukaryotic host cells is facilitated, in part, by the type III secreted effector protein, Tarp. The role of Tarp in chlamydiae entry of host cells is supported by molecular approaches that examined recombinant Tarp or Tarp effectors expressed within heterologous systems. A major limitation in the ability to study the contribution of Tarp to chlamydial invasion of host cells was the prior absence of genetic tools for chlamydiae. Based on our knowledge of Tarp domain structure and function along with the introduction of genetic approaches in C. trachomatis, we hypothesized that Tarp function could be disrupted in vivo by the introduction of dominant negative mutant alleles. We provide evidence that transformed C. trachomatis produced epitope tagged Tarp, which was secreted into the host cell during invasion. We examined the effects of domain specific Tarp mutations on chlamydial invasion and growth and demonstrate that C. trachomatis clones harboring engineered Tarp mutants lacking either the actin binding domain or the phosphorylation domain had reduced levels of invasion into host cells. These data provide the first in vivo evidence for the critical role of Tarp in C. trachomatis pathogenesis and indicate that chlamydial invasion of host cells can be attenuated via the introduction of engineered dominant negative type three effectors.
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Affiliation(s)
- Christopher J Parrett
- Division of Immunology and Pathogenesis, Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida Orlando, FL, USA
| | - Robert V Lenoci
- Division of Immunology and Pathogenesis, Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida Orlando, FL, USA
| | - Brenda Nguyen
- Division of Immunology and Pathogenesis, Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida Orlando, FL, USA
| | - Lauren Russell
- Division of Immunology and Pathogenesis, Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida Orlando, FL, USA
| | - Travis J Jewett
- Division of Immunology and Pathogenesis, Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida Orlando, FL, USA
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de Barsy M, Frandi A, Panis G, Théraulaz L, Pillonel T, Greub G, Viollier PH. Regulatory (pan-)genome of an obligate intracellular pathogen in the PVC superphylum. ISME JOURNAL 2016; 10:2129-44. [PMID: 26953603 PMCID: PMC4989314 DOI: 10.1038/ismej.2016.23] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/10/2015] [Revised: 01/19/2016] [Accepted: 01/21/2016] [Indexed: 01/17/2023]
Abstract
Like other obligate intracellular bacteria, the Chlamydiae feature a compact regulatory genome that remains uncharted owing to poor genetic tractability. Exploiting the reduced number of transcription factors (TFs) encoded in the chlamydial (pan-)genome as a model for TF control supporting the intracellular lifestyle, we determined the conserved landscape of TF specificities by ChIP-Seq (chromatin immunoprecipitation-sequencing) in the chlamydial pathogen Waddlia chondrophila. Among 10 conserved TFs, Euo emerged as a master TF targeting >100 promoters through conserved residues in a DNA excisionase-like winged helix-turn-helix-like (wHTH) fold. Minimal target (Euo) boxes were found in conserved developmentally-regulated genes governing vertical genome transmission (cytokinesis and DNA replication) and genome plasticity (transposases). Our ChIP-Seq analysis with intracellular bacteria not only reveals that global TF regulation is maintained in the reduced regulatory genomes of Chlamydiae, but also predicts that master TFs interpret genomic information in the obligate intracellular α-proteobacteria, including the rickettsiae, from which modern day mitochondria evolved.
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Affiliation(s)
- Marie de Barsy
- Institute of Microbiology, University Hospital Center, University of Lausanne, Lausanne, Switzerland
| | - Antonio Frandi
- Department of Microbiology and Molecular Medicine, Institute of Genetics and Genomics in Geneva (iGE3), Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Gaël Panis
- Department of Microbiology and Molecular Medicine, Institute of Genetics and Genomics in Geneva (iGE3), Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Laurence Théraulaz
- Department of Microbiology and Molecular Medicine, Institute of Genetics and Genomics in Geneva (iGE3), Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Trestan Pillonel
- Institute of Microbiology, University Hospital Center, University of Lausanne, Lausanne, Switzerland
| | - Gilbert Greub
- Institute of Microbiology, University Hospital Center, University of Lausanne, Lausanne, Switzerland
| | - Patrick H Viollier
- Department of Microbiology and Molecular Medicine, Institute of Genetics and Genomics in Geneva (iGE3), Faculty of Medicine, University of Geneva, Geneva, Switzerland
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Rosario CJ, Tan M. Regulation of Chlamydia Gene Expression by Tandem Promoters with Different Temporal Patterns. J Bacteriol 2016; 198:363-9. [PMID: 26527644 PMCID: PMC4751786 DOI: 10.1128/jb.00859-15] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Accepted: 10/24/2015] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED Chlamydia is a genus of pathogenic bacteria with an unusual intracellular developmental cycle marked by temporal waves of gene expression. The three main temporal groups of chlamydial genes are proposed to be controlled by separate mechanisms of transcriptional regulation. However, we have noted genes with discrepancies, such as the early gene dnaK and the midcycle genes bioY and pgk, which have promoters controlled by the late transcriptional regulators EUO and σ(28). To resolve this issue, we analyzed the promoters of these three genes in vitro and in Chlamydia trachomatis bacteria grown in cell culture. Transcripts from the σ(28)-dependent promoter of each gene were detected only at late times in the intracellular infection, bolstering the role of σ(28) RNA polymerase in late gene expression. In each case, however, expression prior to late times was due to a second promoter that was transcribed by σ(66) RNA polymerase, which is the major form of chlamydial polymerase. These results demonstrate that chlamydial genes can be transcribed from tandem promoters with different temporal profiles, leading to a composite expression pattern that differs from the expression profile of a single promoter. In addition, tandem promoters allow a gene to be regulated by multiple mechanisms of transcriptional regulation, such as DNA supercoiling or late regulation by EUO and σ(28). We discuss how tandem promoters broaden the repertoire of temporal gene expression patterns in the chlamydial developmental cycle and can be used to fine-tune the expression of specific genes. IMPORTANCE Chlamydia is a pathogenic bacterium that is responsible for the majority of infectious disease cases reported to the CDC each year. It causes an intracellular infection that is characterized by coordinated expression of chlamydial genes in temporal waves. Chlamydial transcription has been shown to be regulated by DNA supercoiling, alternative forms of RNA polymerase, and transcription factors, but the number of transcription factors found in Chlamydia is far fewer than the number found in most bacteria. This report describes the use of tandem promoters that allow the temporal expression of a gene or operon to be controlled by more than one regulatory mechanism. This combinatorial strategy expands the range of expression patterns that are available to regulate chlamydial genes.
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Affiliation(s)
- Christopher J Rosario
- Department of Microbiology and Molecular Genetics, University of California, Irvine, California, USA
| | - Ming Tan
- Department of Microbiology and Molecular Genetics, University of California, Irvine, California, USA Department of Medicine, University of California, Irvine, California, USA
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Orillard E, Tan M. Functional analysis of three topoisomerases that regulate DNA supercoiling levels in Chlamydia. Mol Microbiol 2015; 99:484-96. [PMID: 26447825 DOI: 10.1111/mmi.13241] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/04/2015] [Indexed: 02/01/2023]
Abstract
Chlamydia is a medically important bacterium that infects eukaryotic cells. Temporal expression of chlamydial genes during the intracellular infection is proposed to be regulated by changes in DNA supercoiling levels. To understand how chlamydial supercoiling levels are regulated, we purified and analyzed three putative Chlamydia trachomatis topoisomerases. As predicted by sequence homology, CT189/190 are the two subunits of DNA gyrase, whereas CT643 is a topoisomerase I. CT660/661 have been predicted to form a second DNA gyrase, but the reconstitute holoenzyme decatenated and relaxed DNA, indicating that the proteins are subunits of topoisomerase IV. Promoter analysis showed that each topoisomerase is transcribed from its own operon by the major chlamydial RNA polymerase. Surprisingly, all three topoisomerase promoters had higher activity from a more supercoiled DNA template. This supercoiling-responsivesness is consistent with negative feedback control of topoisomerase I and topoisomerase IV expression, which is typical of other bacteria. However, activation of the chlamydial gyrase promoter by increased supercoiling is unorthodox compared with the relaxation-induced transcription of gyrase in other bacteria. We present a model in which supercoiling levels during the intracellular chlamydial developmental cycle are regulated by unusual positive feedback control of the gyrase promoter and the temporal expression of three topoisomerases.
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Affiliation(s)
- Emilie Orillard
- Department of Microbiology and Molecular Genetics, University of California, Irvine, CA, USA
| | - Ming Tan
- Department of Microbiology and Molecular Genetics, University of California, Irvine, CA, USA.,Department of Medicine, University of California, Irvine, CA, USA
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Shen L, Macnaughtan MA, Frohlich KM, Cong Y, Goodwin OY, Chou CW, LeCour L, Krup K, Luo M, Worthylake DK. Multipart Chaperone-Effector Recognition in the Type III Secretion System of Chlamydia trachomatis. J Biol Chem 2015; 290:28141-28155. [PMID: 26438824 DOI: 10.1074/jbc.m115.670232] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2015] [Indexed: 11/06/2022] Open
Abstract
Secretion of effector proteins into the eukaryotic host cell is required for Chlamydia trachomatis virulence. In the infection process, Scc1 and Scc4, two chaperones of the type III secretion (T3S) system, facilitate secretion of the important effector and plug protein, CopN, but little is known about the details of this event. Here we use biochemistry, mass spectrometry, nuclear magnetic resonance spectroscopy, and genetic analyses to characterize this trimolecular event. We find that Scc4 complexes with Scc1 and CopN in situ at the late developmental cycle of C. trachomatis. We show that Scc4 and Scc1 undergo dynamic interactions as part of the unique bacterial developmental cycle. Using alanine substitutions, we identify several amino acid residues in Scc4 that are critical for the Scc4-Scc1 interaction, which is required for forming the Scc4·Scc1·CopN ternary complex. These results, combined with our previous findings that Scc4 plays a role in transcription (Rao, X., Deighan, P., Hua, Z., Hu, X., Wang, J., Luo, M., Wang, J., Liang, Y., Zhong, G., Hochschild, A., and Shen, L. (2009) Genes Dev. 23, 1818-1829), reveal that the T3S process is linked to bacterial transcriptional events, all of which are mediated by Scc4 and its interacting proteins. A model describing how the T3S process may affect gene expression is proposed.
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Affiliation(s)
- Li Shen
- Department of Microbiology, Immunology, and Parasitology.
| | - Megan A Macnaughtan
- Department of Chemistry, Louisiana State University, Baton Range, Louisiana 70803
| | | | - Yanguang Cong
- Department of Microbiology, Immunology, and Parasitology
| | - Octavia Y Goodwin
- Department of Chemistry, Louisiana State University, Baton Range, Louisiana 70803
| | - Chau-Wen Chou
- Department of Chemistry, University of Georgia, Athens, Georgia 30602
| | - Louis LeCour
- Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, New Orleans, Louisiana 70112
| | - Kristen Krup
- Department of Microbiology, Immunology, and Parasitology
| | - Miao Luo
- Department of Microbiology, Immunology, and Parasitology
| | - David K Worthylake
- Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, New Orleans, Louisiana 70112
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Rosario CJ, Hanson BR, Tan M. The transcriptional repressor EUO regulates both subsets of Chlamydia late genes. Mol Microbiol 2014; 94:888-97. [PMID: 25250726 DOI: 10.1111/mmi.12804] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/21/2014] [Indexed: 01/07/2023]
Abstract
The pathogenic bacterium Chlamydia replicates in a eukaryotic host cell via a developmental cycle marked by temporal waves of gene expression. We have previously shown that late genes transcribed by the major chlamydial RNA polymerase, σ(66) RNA polymerase, are regulated by a transcriptional repressor EUO. We now report that EUO also represses promoters for a second subset of late genes that are transcribed by an alternative polymerase called σ(28) RNA polymerase. EUO bound in the vicinity of six σ(28) -dependent promoters and inhibited transcription of each promoter. We used a mutational analysis to demonstrate that the EUO binding site functions as an operator that is necessary and sufficient for EUO-mediated repression of σ(28) -dependent transcription. We also verified specific binding of EUO to σ(66) -dependent and σ(28) -dependent promoters with a DNA immunoprecipitation assay. These findings support a model in which EUO represses expression of both σ(66) -dependent and σ(28) -dependent late genes. We thus propose that EUO is the master regulator of late gene expression in the chlamydial developmental cycle.
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Affiliation(s)
- Christopher J Rosario
- Department of Microbiology and Molecular Genetics, University of California, Irvine, CA, USA
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Croxatto A, Murset V, Chassot B, Greub G. Early expression of the type III secretion system of Parachlamydia acanthamoebae during a replicative cycle within its natural host cell Acanthamoeba castellanii. Pathog Dis 2013; 69:159-75. [PMID: 23861207 DOI: 10.1111/2049-632x.12065] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2013] [Revised: 06/28/2013] [Accepted: 07/01/2013] [Indexed: 12/26/2022] Open
Abstract
The type three secretion system (T3SS) operons of Chlamydiales bacteria are distributed in different clusters along their chromosomes and are conserved at both the level of sequence and genetic organization. A complete characterization of the temporal expression of multiple T3SS components at the transcriptional and protein levels has been performed in Parachlamydia acanthamoebae, replicating in its natural host cell Acanthamoeba castellanii. The T3SS components were classified in four different temporal clusters depending on their pattern of expression during the early, mid- and late phases of the infectious cycle. The putative T3SS transcription units predicted in Parachlamydia are similar to those described in Chlamydia trachomatis, suggesting that T3SS units of transcriptional expression are highly conserved among Chlamydiales bacteria. The maximal expression and activation of the T3SS of Parachlamydia occurred during the early to mid-phase of the infectious cycle corresponding to a critical phase during which the intracellular bacterium has (1) to evade and/or block the lytic pathway of the amoeba, (2) to differentiate from elementary bodies (EBs) to reticulate bodies (RBs), and (3) to modulate the maturation of its vacuole to create a replicative niche able to sustain efficient bacterial growth.
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Affiliation(s)
- Antony Croxatto
- Center for Research on Intracellular Bacteria (CRIB), Institute of Microbiology, University Hospital Center and University of Lausanne, Lausanne, Switzerland
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Rosario CJ, Tan M. The early gene product EUO is a transcriptional repressor that selectively regulates promoters of Chlamydia late genes. Mol Microbiol 2012; 84:1097-107. [PMID: 22624851 DOI: 10.1111/j.1365-2958.2012.08077.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The obligate intracellular bacterium Chlamydia has an unusual developmental cycle in which there is conversion between two forms that are specialized for either intracellular replication or propagation of the infection to a new host cell. Expression of late chlamydial genes is upregulated during conversion from the replicating to the infectious form, but the mechanism for this temporal regulation is unknown. We found that EUO, which is expressed from an early gene, binds to two sites upstream of the late operon omcAB, but only the downstream site was necessary for transcriptional repression. Using gel shift and in vitro transcription assays we showed that EUO specifically bound and repressed promoters of Chlamydia trachomatis late genes, but not early or mid genes. These findings support a role for EUO as a temporal repressor that negatively regulates late chlamydial genes and prevents their premature expression. The basis of this specificity is the ability of EUO to selectively bind promoter regions of late genes, which would prevent their transcription by RNA polymerase. Thus, we propose that EUO is a master regulator that prevents the terminal differentiation of the replicating form of chlamydiae into the infectious form until sufficient rounds of replication have occurred.
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Affiliation(s)
- Christopher J Rosario
- Departments of Microbiology and Molecular Genetics Medicine, University of California, Irvine, CA 92697-4025, USA
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Differential effects of DNA supercoiling on Chlamydia early promoters correlate with expression patterns in midcycle. J Bacteriol 2012; 194:3109-15. [PMID: 22505684 DOI: 10.1128/jb.00242-12] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022] Open
Abstract
Changes in DNA supercoiling levels during the chlamydial developmental cycle have been proposed as a global mechanism to upregulate midcycle genes, but the effects on early genes are not known. We examined the promoters for 10 Chlamydia trachomatis early genes and found that they could be separated into two subsets based on their responses to DNA supercoiling in vitro. Furthermore, the type of supercoiling response correlated with the in vivo expression pattern for each early gene. One subset of seven early genes had promoters that were transcribed in a supercoiling-insensitive manner over the physiologic range of supercoiling levels that have been measured in Chlamydia. In vivo transcripts for these genes were detected at similar levels during early-stage and midstage times. In contrast, a second subset, represented in our study by three early genes, had supercoiling-dependent promoters that were transcribed at higher levels from more-supercoiled templates, which is the response observed for midcycle genes. Genes in this subset were expressed at higher levels at midstage times than at early times in vivo. We propose that this second subset represents a novel class of chlamydial developmental genes with features of both early and midcycle genes. We hypothesize that expression of these supercoiling-dependent early genes is upregulated by increased chlamydial supercoiling levels in midcycle via their supercoiling-responsive promoters in a manner similar to that for midcycle genes. Thus, we propose that DNA supercoiling is utilized in Chlamydia as a general mechanism to regulate genes in the midstage of the developmental cycle and not just midcycle genes.
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The atypical OmpR/PhoB response regulator ChxR from Chlamydia trachomatis forms homodimers in vivo and binds a direct repeat of nucleotide sequences. J Bacteriol 2010; 193:389-98. [PMID: 21057008 DOI: 10.1128/jb.00833-10] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Two-component signal transduction systems are widespread in bacteria and are essential regulatory mechanisms for many biological processes. These systems predominantly rely on a sensor kinase to phosphorylate a response regulator for controlling activity, which is frequently transcriptional regulation. In recent years, an increasing number of atypical response regulators have been discovered in phylogenetically diverse bacteria. These atypical response regulators are not controlled by phosphorylation and exhibit transcriptional activity in their wild-type form. Relatively little is known regarding the mechanisms utilized by these atypical response regulators and the conserved characteristics of these atypical response regulators. Chlamydia spp. are medically important bacteria and encode an atypical OmpR/PhoB subfamily response regulator termed ChxR. In this study, protein expression analysis supports that ChxR is likely exerting its effect during the middle and late stages of the chlamydial developmental cycle, stages that include the formation of infectious elementary bodies. In the absence of detectable phosphorylation, ChxR formed homodimers in vitro and in vivo, similar to a phosphorylated OmpR/PhoB subfamily response regulator. ChxR was demonstrated to bind to its own promoter in vivo, supporting the role of ChxR as an autoactivator. Detailed analysis of the ChxR binding sites within its own promoter revealed a conserved cis-acting motif that includes a tandem repeat sequence. ChxR binds specifically to each of the individual sites and exhibits a relatively large spectrum of differential affinity. Taken together, these observations support the conclusion that ChxR, in the absence of phosphorylation, exhibits many of the characteristics of a phosphorylated (active) OmpR/PhoB subfamily response regulator.
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Betts-Hampikian HJ, Fields KA. The Chlamydial Type III Secretion Mechanism: Revealing Cracks in a Tough Nut. Front Microbiol 2010; 1:114. [PMID: 21738522 PMCID: PMC3125583 DOI: 10.3389/fmicb.2010.00114] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2010] [Accepted: 09/22/2010] [Indexed: 12/22/2022] Open
Abstract
Present-day members of the Chlamydiaceae contain parasitic bacteria that have been co-evolving with their eukaryotic hosts over hundreds of millions of years. Likewise, a type III secretion system encoded within all genomes has been refined to complement the unique obligate intracellular niche colonized so successfully by Chlamydia spp. All this adaptation has occurred in the apparent absence of the horizontal gene transfer responsible for creating the wide range of diversity in other Gram-negative, type III-expressing bacteria. The result is a system that is, in many ways, uniquely chlamydial. A critical mass of information has been amassed that sheds significant light on how the chlamydial secretion system functions and contributes to an obligate intracellular lifestyle. Although the overall mechanism is certainly similar to homologous systems, an image has emerged where the chlamydial secretion system is essential for both survival and virulence. Numerous apparent differences, some subtle and some profound, differentiate chlamydial type III secretion from others. Herein, we provide a comprehensive review of the current state of knowledge regarding the Chlamydia type III secretion mechanism. We focus on the aspects that are distinctly chlamydial and comment on how this important system influences chlamydial pathogenesis. Gaining a grasp on this fascinating system has been challenging in the absence of a tractable genetic system. However, the surface of this tough nut has been scored and the future promises to be fruitful and revealing.
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